A heat exchanger assembly includes an outlet header extending along an outlet axis to define an outlet cavity and an inlet header defining an inlet cavity. A plurality of refrigerant tubes extends from the inlet header through the outlet header and into the outlet cavity. A collector conduit having a generally semi-circular conduit cross-section defining an arced surface and a chord surface interconnected with rounded ends is disposed in the outlet header and includes a conduit body portion and at least one conduit end portion interconnected by a conduit transition portion with the conduit body portion being offset from the conduit end portion. The conduit body portion is engaged to an interior surface of the outlet header to space the conduit body portion from the refrigerant tubes and the conduit end portion is coaxial with the outlet header axis to provide a central outlet for the refrigerant vapor.